1. Field of the Invention
The present invention relates to a signal transfer device for switching and transferring communication signals and carrying out transfer processing of control information to perform switching and transferring; in particular, the present invention relates to a transfer device for transferring control information in a signal transfer device by detecting a trouble and discriminating control information in a communication signal and sending said trouble and control information using incoming/outgoing packages which differ according to the switching mode.
2. Description of the Related Arts
The switching mode such as cross-connect, add-drop and non-symmetrical switchings have been used within a telecommunications network. Therefore, it has been necessary for a transfer device to transfer control information in a telecommunications network to detect trouble and discriminate control information and transfer them using incoming/outgoing packages which differ according to the switching modes of the telecommunications network.
FIG. 1 is a diagram showing a conventional configuration example to explain a conventional transfer device including transference of trouble and control information.
The transfer device depicted in the diagram is an asynchronous transfer mode (hereinafter ATM) transfer device 300 having incoming sections 301-303, a cross-connecting switching section 307 and outgoing sections 304-306.
In this example there are 3 incoming sections and corresponding virtual paths (hereinafter VP) VP1, VP2 and VP3, VP1 is connected from incoming section 301 to outgoing section 305 via the switching section 307, VP2 is connected at incoming section 302 and virtual channels (hereinafter VC) VC1 and VC2 are extracted from VP2. Similarly, VC3 and VC4 are extracted from VP3 at incoming section 303.
The communication signals are switched at the switching section 307, such a way that VC1 and VC3 are connected to outgoing stage 304 and multiplexed to form VP4, VC2 and VC4 are connected to outgoing stage 306 and multiplexed to form VP5, thereby VP1, VP4 and VP5 are transmitted to succeeding nodes.
When the optical fibers accommodating VP1 and VP3 is disconnected, a detector 311 in the incoming section 301 detects the disconnection (hereinafter LOS) and outgoing section 305 is notified the LOS via the main VP1 signal. At outgoing section 305, an inserter inserts a VC-AIS (VC Alarm Indication Signal) control signal to the communication signal.
Furthermore, incoming stage 303 notifies outgoing sections 304 and 306 and these outgoing sections 304 and 306 insert VC-AIS control signals to the communication signals.
Thus the notification destination of trouble differs according to the switching modes that is how the communication signal is switched at switching section 307. This switching modes are a cross-connection switching node, an add-drop switching mode and a non-symmetrical switching mode.
In other words, the add-drop switching mode is included in the cross-connection switching mode which switches a required signal from the aggregate side to the tributary side or vice versa. In the non-symmetrical switching mode, a switching section switches between un-symmetric numbers of ports (hereinafter "multi-casts"), for instance, between a single incoming section and multiple outgoing sections.
Since the reciprocal relationships between the incoming and outgoing sections vary depending on the switching mode in the telecommunications network, detection of control information (e.g. LOS) at a transfer device and transmission of control signals (e.g. AIS) from the outgoing sections must be performed in accordance with these varying relations between the incoming and outgoing sections.
In other words, the notification destinations of control information in the transfer device can be flexibly served.
An AIS signal transmission system for a telecommunications network disclosed in Journal of Technical Disclosure (JIII) by Japan Invention Association Lay-out No. 5977/93 is shown in FIG. 1 as a concrete first conventional example. In this case, control information are placed in the respective main signals.
In other words, since a required control information is automatically placed within a main communication signal at the incoming section prior to be transferred and transmitted without being changed, no special control is needed within the device for transference and the control information can be transferred and transmitted at high speed.
The advantage of the above-mentioned conventional example is that there is no need for indicating the transfer destination of control information designating which control information should be placed on which main signal at the incoming section, but there is the possibility that the through-put of the main signal will be adversely affected as explained below.
FIG. 2 shows a second conventional example disclosed in JIII Lay-out No. 5977/93 wherein transmission of the control information is carried out via a third party, which is in this case a control center.
The advantage of this second conventional example is that there is no influence on the through-put of the main signal as in the first conventional example, since the required control information is not inserted into the main signal but is transmitted through the control center.
In addition, a third conventional example is that disclosed in Japanese Patent Application Lay-out No. 165846/92. The object of this third conventional example is to reduce the amount of processing within the transfer device by means of an alarm transfer method wherein each transfer device has a distributed path setting table in advance from a network control center and when a fault occurs, an appropriate path setting is carried out in compliance with the path setting table.
However, when transferring control information by the way of any of the above conventional examples, the following problems are arisen.
According to the first conventional example, there is no band increase caused by the control information transfer in synchronous transfer mode (hereinafter STM), but in ATM, the control information transfer causes an increase in the number of frequency bands and thereby reduces the through-put of the main signal as it passes through the switching section.
According to the second conventional example, as explained in JIII Lay-out No. 5977/93, data indicating the transfer destination of control information are managed at a control center and when a great number of control signals have to be transferred simultaneously, processings of data indicating the transfer destination are concentrated in this control center resulting that control information cannot be transferred at high speed; if high speed transfer is required, the concentrated considerable processings at the control center request high physical costs and increase of power consumption.